Dynamic fixation stimuli for visual field testing and therapy

ABSTRACT

Alteration of a fixation or peripheral stimulus displayed on a computer-driven display allows a human subject to maintain extended visual fixation upon the resulting dynamic stimulus. The fixation is presented upon the display and the stimulus is altered to allow resensitization of the subject&#39;s retina, thereby allowing prolonged visual fixation upon the resulting dynamic target. A dynamic stimulus may utilize a frequency doubling illusion.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application claims priority from U.S. ProvisionalApplication Ser. No. 60/833,199 filed on Jul. 25, 2006 and U.S.Provisional Application Ser. No. 60/867,499 filed on Nov. 28, 2006,which are hereby incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to systems for maintaining the focus of asubject on a specified region of a display for purposes of testing orimproving a subject's vision.

BACKGROUND

The macula is the region of the retina which is used for high acuityvision, as is typically required for reading. To diagnose maculardamage, a patient may undergo various types of examinations, includingautomated perimetry or campimetry, in which the patient is positioned infront of a test surface and is asked to maintain focus on a target. Acomputer then actuates one or more light sources to present visualstimuli at specific points on the test surface. The patient is asked topress a button in response to perceived test stimuli and the examiner orcomputer records the patient input and associated spatial information.In this way a visual field map is created.

The human retina is unable to fixate continuously upon an unmoving,unchanging stimulus. After less than a second of stimulation, thesubject's retinal cells will adapt to the stimulus and no longer relayany information to the brain regarding the stimulus. Such adaptation isproblematic for devices requiring constant fixation upon a fixed pointsince the viewer must change fixation in order to continue seeing theobject of regard. This changing fixation may reduce the accuracy,precision, and overall effectiveness of testing, therapeutic, ornon-therapeutic visual stimulation programs that require continuousunchanging visual fixation.

The human visual system includes two simultaneously functioningpathways. The more primitive “M” pathway is dedicated largely to therecognition of moving objects or objects that change in luminosity. The“P” pathway is more evolved and more closely coupled to neuralstructures associated with conscious thought. The “P” pathway providesrecognition of fine detail and color to the brain and is much lesscommitted to motion detection.

In persons who have suffered damage to the visual system (which includesthe brain itself), these two pathways frequently are affected todifferent degrees. Moreover, the two systems usually recover function atdifferent rates. This disparity of functional loss and recovery cancause significant disharmony of the innately matched systems andresulting disturbances to the overall sensory function of the subject.

The ability to accurately detect the different types of visualprocessing disturbance and to properly treat the affected pathways is ofvital importance to the treating practitioner and ultimately, thepatient. Increased diagnostic testing sensitivity and visual therapyspecificity result in better prognosis for recovery of the individual'sfunction. Current diagnostic testing modalities are limited in theirability to detect specific types of visual function damage.

Most field-of-vision testing falls into one of two categories: Staticperimetry and kinetic perimetry. Static perimetry is valuable inestablishing a depiction of fine light sensitivity or detail within thecentral 30 to 60 degrees of visual field (“P” cell function), whilekinetic perimetry is valuable in identifying the borders of motionvision function (“M” cell function). However, neither technique is ableto identify efficiently the amount or level of motion sensitivity at allthe points within the borders.

In static perimetry, the patient fixates upon a specific point whilelight stimuli (spots) are delivered to various points in the peripheralvisual field. Static perimetry can be administered using peripheralstimuli of varying brightness to determine the level of luminancesensitivity throughout the field, or with peripheral stimuli ofidentical brightness, to screen for the presence or absence of vision atvarious locations.

Kinetic perimetry also requires a patient to fixate a central spotduring delivery of peripheral stimuli. In kinetic perimetry, the stimuliare luminous spots of varying size and brightness. The spots are movedfrom an area where there is known to be no vision (e.g. the farperiphery or physiologic blind spot) toward areas where vision mayexist. The patient is tasked with responding upon detection of a movinglight in the periphery. Test points are delivered along radii of thecircle (or “horopter”) of the patient's field of vision. The points offirst detection are recorded on a plot and the circumference of theconnected points is considered the border of motion and lightsensitivity for the brightness and size of the stimulus used.

Frequency doubling technology (FDT) is used to test the spatialresolution of a subject's visual field. In FDT, a subject attempts toobserve a peripheral square or circular grating comprised of striationsof alternating luminosities. The gratings are modulated in a wavepattern involving temporal changes in luminosity of the striations. Theluminosity modulation is performed above the critical flicker frequency(CFF), typically about 25 Hz, so that the modulation is not noticeableto the subject. If the subject's visual field is sufficient, the subjectwill observe an optical illusion in which the spatial frequency of thestriations is doubled, i.e., the space between the striations is halved.The spatial frequency or contrast may be modulated to determine thelimits of the subject's spatial resolution. In a patient with visualfield damage, e.g., one suffering from glaucoma, an abnormally lowspatial frequency may be required for the subject to observe thefrequency doubling illusion. In U.S. Pat. No. 6,068,377, issued May 30,2000 to McKinnon, an alternate version of FDT is employed, in which thegrating is isoluminous, but with alternating hue.

Work in the laboratory of Krystel R. Huxlin at the University ofRochester has utilized a series of spot stimuli for visual fieldtherapy. In the poster presentation, “Training-induced perceptualrecovery after visual cortical stroke” Eric Kelts, Jennifer M. Williams,Brad Feldman, Mary Hayhoe and Krystel R. Huxlin, 30^(th) Annual NANOSmeeting, Orlando, Fla., 2004, stimuli move with respect to the entirevisual field. Such as approach is not consistent with visual restorationtherapy approaches that individually target small regions of the visualfield. Additionally, movement of a stimulus across a large region willtend to cause distraction of a patient, and is thus inconsistent withvisual therapy approaches that utilize a fixation stimulus. If patientfeedback were collected with such a system, it would be difficult oreven impossible to precisely locate the visual filed region that causedthe patient's perception to be triggered.

SUMMARY OF THE INVENTION

In accordance with an embodiment of the invention, alteration of afixation stimulus displayed on a computer-driven display allows a humansubject to maintain extended visual fixation upon the resulting dynamicstimulus. The fixation is presented upon the display and the stimulus isaltered to allow resensitization of the subject's retina, therebyallowing prolonged visual fixation upon the resulting dynamic target.

In accordance with various embodiments, the steps of presenting thestimulus and altering the stimulus may be repeated for a given number ofcycles top allow sustained sensitization and prolonged fixation by thesubject. The fixation of the subject may be verified by presenting atest cue and recording a subject's input in response to the test cue.Like the dynamic fixation stimulus, the test cue may also be altered toallow resensitization of the subject's retina.

In order to prevent the subject from predicting the time at which a testcue is presented, successive presentation of the test cue may beperformed with varying intervening time intervals. One way to vary thetime intervals is to vary the number of cycles of presentation of thefixation stimulus and the altered fixation stimulus.

In accordance with particular embodiments, the alteration of the dynamicfixation stimulus is visible only by using a portion of the subject'sretina corresponding to about 2 degrees or less of the subject's centralvisual field.

There are many suitable fixation stimulus geometries and dynamictransformations. For example, the fixation stimulus may have the form ofa repetitively translating object, a rotating object, or an intermingledset of cyclically changing objects. The stimulus could include two setsof intermingled striations of opposite and cyclically alteringluminosities.

In embodiments of the invention, the dynamic fixation stimulus is usedfor purposes of vision testing or training.

In related embodiments, a method is provided for stimulating amotion-detecting visual pathway of a subject. A subject is tasked withfixating on a central stimulus displayed on a computer-driven display.While the subject is visually fixated, a peripheral stimulus ispresented on the display. At least one characteristic of the peripheralstimulus is altered so as to trigger the motion-sensitive visual pathwayof the subject.

In other related embodiments, the altered characteristic may be thespatial locus, size, pattern, luminosity or hue of the stimulus. Thealtered and base stimulus may be alternately displayed in a cyclicalmanner to sustain the display of a dynamic peripheral stimulus. Whilealternately displaying the base and altered stimulus, the subject'sresponse, indicative of their detection of the stimulus, may bemonitored and recorded. The dynamic peripheral stimulus may be, forexample, a repetitively translating object, or a repetitively blinkingobject. By first determining the bounds of a subject's visual field,testing or therapy can be concentrated within those bounds.

In further related embodiments, a computer program product for use on acomputer system is provided for stimulating motion-sensitive regions ofa subject's peripheral vision. The computer program includes a computerusable medium having computer readable program code, which includesprogram code for providing a dynamic peripheral stimulation displayedupon a computer-driven display and program code for recording thesubject's response to the dynamic peripheral stimulation.

In accordance with another embodiment of the invention, a method isprovided for maintaining fixation for purposes of testing or treatingthe visual field of a subject; the method may also be implemented in acomputer system or computer program product. The method includes thesteps of providing a fixation stimulus for the subject to visuallyfixate upon, repeatedly altering the stimulus to create an opticalillusion that is only detectable by use of the subject's central visualfield and presenting a peripheral stimulus to the subject while thesubject is fixated on the fixation stimulus. The subject's response tothe peripheral stimulus may be recorded.

In related embodiments, the difficulty level of the optical illusion istuned to match the spatial perception ability of the subject. Theoptical illusion may be a frequency doubling optical illusion, such as afrequency doubling grating. The difficulty level of the frequencydoubling grating may be tuned by altering the spatial frequency of thegrating. For example, the tuning process may include increasing thespatial frequency of the grating until the illusion is not properlydetected by the subject and then maintaining the spatial frequency at alevel that is detectable by the subject, yet near the limit of thespatial resolution of the subject's central visual field. The fixationstimulus may be systematically altered to target different retinalregions, for example, by rotation or translation, thereby preventingdesensitization. A fixation test cue may be presented to query thesubject's fixation upon the stimulus.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of the invention will be more readily understoodby reference to the following detailed description, taken with referenceto the accompanying drawings, in which:

FIG. 1 shows a flow chart of a method for presenting a dynamic fixationstimulus in accordance with an embodiment of the invention;

FIG. 2 shows a flow chart of a method for presenting a base andalternate dynamic fixation stimulus in accordance with an anotherembodiment of the invention;

FIG. 3 shows a flow chart of a method for presenting a base andalternate dynamic fixation stimulus in accordance with the embodiment ofFIG. 2;

FIGS. 4-10 show a repetitively translating fixation stimulus inaccordance with an embodiment of the invention;

FIGS. 11-17 show a rotating fixation stimulus in accordance with anotherembodiment of the invention;

FIG. 18 shows a grating-like dynamic fixation stimulus in accordancewith yet another embodiment of the invention, at a first time point;

FIG. 19 shows a grating-like stimulus in accordance with the embodimentof FIG. 18 at a second time point;

FIG. 20 is a flow chart of a method for creating a dynamic peripheralstimulus and recording a subject's response to the stimulus.

FIG. 21 shows a frequency doubling grating fixation stimulus asdisplayed on a computerized display;

FIG. 22 shows the frequency doubling grating fixation stimulus of FIG.21, as perceived by a subject;

FIG. 23 is a flow chart for a method of tuning and using the frequencydoubling grating fixation stimulus of FIGS. 21-22.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS

Definitions. As used in this description and the accompanying claims,the following terms shall have the meanings indicated, unless thecontext otherwise requires:

“Visual Restoration Therapy” shall mean a process for allocating andtargeting light stimuli to particular regions of a patient's visualfield.

A “subject” shall mean a human receiving light stimuli during a visualrestoration therapy session.

In illustrative embodiments of the invention, a dynamic stimulus ispresented via a computer-driven display for a human subject (e.g., apatient or trainee) to fixate upon. At least a portion of the dynamicfixation stimulus is periodically altered in appearance, to mitigate thestimulation to corresponding retinal regions and facilitating retinalresensitization. Accordingly, the subject should be able to avoidretinal adaptation and sustain fixation upon the stimulus for longerthan would typically be achievable or comfortable with a staticstimulus. When used as a central target in perimetry, campimetry, orvision enhancing training (e.g. vision restoration therapy targetingperipheral regions), the dynamic fixation stimulus may help to increasethe accuracy, precision, reproducibility, and effectiveness of theprocedure. In some embodiments, the dynamic changes in the stimulus mayonly be observed using the central portion of a subject's visual field.Embodiments may be implemented using a computerized display withappropriate software routines according to methods disclosed herein.Computer based systems for implementing visual restoration therapy arecommercialized by the assignee, NovaVision Inc. of Boca Raton, Fla. U.S.Pat. No. 6,464, 356 and U.S. Patent Application publication nos.2005-0213033, 2006-0092377, 2006-0283466, 2007-0038142 all disclosecomputer based systems for visual restoration therapy and are herebyincorporated by reference herein.

In related embodiments of the invention, a dynamic stimulus is used as aperipheral spot stimulus for purposes of visual field mapping ortherapy. The dynamic peripheral stimulus is presented upon a region of adisplay to target a corresponding peripheral region of the visual fieldand preferentially activates the motion-detecting cells and/orstructures (e.g., the M pathway) in that region of the visual field.When used with visual restoration therapy, perimetry, or campimetry, thedynamic peripheral stimulus allows measurement and/or therapeuticstimulation of motion-detection pathway function. Unlike stimuli of theprior art that move in a pattern across all or large portions of thevisual field, dynamic peripheral stimuli of the present invention areconfined to subregions of the visual field in a manner that makes themcompatible with targeted stimulation of the M pathway in small regionsthat may be defined or located with respect to a fixation stimulus.Embodiments include using dynamic peripheral stimuli that are“animations” within narrowly bounded zones that are of a size comparableto traditional spot stimuli and moving the bounds of the animation to asecond location. Patient responses to the animated stimuli may berecorded upon presentation of each dynamic peripheral stimulus.

FIG. 1 shows a flow chart, which summarizes a method in accordance withan embodiment of the invention. A base fixation stimulus is presented ona computer display (step 100). Although usually presented in the centerof the display, the stimulus could also be presented off-center tobetter target a particular region of the visual field for testing ortraining. After presenting the base stimulus for a period of time, allor part of the stimulus is altered (step 110) in a manner that shouldallow resensitization of the subject's retina. The altered stimulus maybe presented on a location of the display that is superimposed upon thebase stimulus, or slightly offset, so that fixation may be readilymaintained on the same area of the display. The area of fixation istypically small, relative to the size of the display (e.g, less than 5%or 1% of the display area). Resensitization may be accomplished byreducing the overall luminosity (brightness), or spectral distributionof luminosity (i.e., color) of all or part of the stimuli, which mayadvantageously lower stimulation of corresponding retinal regions. Afterpresenting the altered stimulus for a time, one or more additionalaltered stimuli may be presented, or the base stimulus may presentedagain by repeating step 100. The resulting loop may be repeated for anumber of iterations, until a condition is fulfilled (e.g., completionof testing, or adequate subject performance) or an interrupt isencountered. The timing of the presentation of the base and alteredstimuli may be adjusted to minimize retinal desensitization; forexample, stimuli may be switched on a sub-second basis. As a result ofthe repeated resensitizations, that part of the subject's visual fieldthat detects the fixation stimulus should be in a condition of sustainedsensitization, thereby allowing for prolonged fixation upon thestimulus.

The repetition between the base and alternate stimuli may cycle, forexample, at a frequency between 0.5 and 100 Hz, and more particularlymay be between 1 Hz and 10 Hz. For example, the cycle may have afrequency of about 3 Hz, with stimuli presented for period of about 150ms. However, the cycles need not be regular; the delay between changesin the stimulus may vary from cycle to cycle, but the majority of suchdelays are typically consistent with the above ranges to allow forsustained sensitization. The delays could increase with time, decreasewith time, follow a pseudo-random sequence, or other pattern. Forexample, the sequence of delays could be 210 ms, 240 ms, 275 ms, 255 ms,etc.

FIGS. 2-3 show flow charts corresponding to embodiments for presenting adynamic fixation stimulus to a subject and testing the subject forfixation. As in the embodiment of FIG. 1, a loop is employed; a basestimulus is displayed for a time period (step 100), an altered stimulus(step 110) is displayed for a time period, and the process is repeated.After a given number (designated by the variable n) of loop cycles, afixation test cue is presented (step 200). The test cue may consist ofchanging the shape, color, pattern or other visually detectable featureof the dynamic fixation stimulus. The subject may be instructed torespond to the test cue through a computer-input device, such as akeyboard, mouse, touchscreen, joystick, microphone, etc. Varying nbetween cycles of alternately presenting the fixation stimulus and testcue may advantageously cause the test cue to be presented at times thatare not readily predictable by the subject, further ensuring subjectcompliance with regard to fixation. However, the timing of test cuepresentation may be varied in other ways, including by altering theduration of base or alternate stimulus presentation. As shown in theflow chart of FIG. 3, the test cue may be altered (step 210) as well, tofacilitate continued fixation upon the test cue. Responses may bereceived from the subject during periods in which either the test cue oraltered test cue are displayed. The test cue and altered test cue may bealternately displayed in a loop (steps 200-210) which may repeat anumber of times, designated by the variable q. As is true fordetermining n, q may be determined in a number of ways and may be eitherfixed or varied. For example, the test cue and alternate test cue may beiteratively displayed (steps 200-210) until a response is received fromthe subject or may simply be displayed for a given number of cycles, orfor a given elapsed time. In any case, after the test cue presentationphase is complete, the base and altered fixation stimulus may again bedisplayed (steps 100-110).

FIGS. 4-10 schematically show, in time-sequence, an embodiment of adynamic fixation stimulus and fixation test cue that utilizes arepetitively translating fixation stimulus presented on a computerizeddisplay. As shown, the translating stimulus 300 is a green oval whichhorizontally translates between a first position (position A, shown inFIGS. 4, 6, 7, and 10), and a second position (position B, shown inFIGS. 5, 8 and 9). Although shown as having a higher luminosity than itsbackground 310, the translating stimulus may also be darker than thebackground. Generally, the translating stimulus should contrastsufficiently with the background so that it is detectable by the subject(though the level of contrast may also be varied during a procedure orcourse of therapy). Of course, the translating stimulus 300 need not bean oval, but could be a any of a variety of shapes and may translatehorizontally, diagonally, or alternately in various directions orpatterns. The stimulus 300 may have any of a variety of colors andpatterns.

As shown in FIGS. 7 and 8, a fixation test cue 400 may be presented atvarious times. The subject may be instructed to respond to theappearance of the fixation test cue 400 via a computer input device. Inthis way, maintenance of visual fixation upon the stimulus 300 may betracked and/or measured. As shown by way of example, the fixation testcue 400 is a change in color of the translating oval from green toyellow, but could be any change in visually detectable characteristics,including a change in shape or movement-pattern of the stimulus.Optionally, the fixation test cue may also be translated; FIG. 7 showsthe fixation test cue in a left (base) position and FIG. 8 shows thefixation test cue in a right (alternate) position. In this way, thefixation test cue may remain visible for a longer period of time.

In accordance with an embodiment of the invention, the timing of thetranslational movement may be performed at a variety of regular, orirregular timings; by way of example, the timing is based on a regularcycle of 2 Hz. In other words, the stimulus 300 is translated aboutevery 250 ms. The following table lists the position, time and color ofthe stimulus, and corresponding figures: Time TranslationalCorresponding (ms) Position Color Figure Comment 0 Left Green 4 Basestimulus 250 Right Green 5 Altered stimulus 500 Left Green 6 750 RightGreen Not shown 1000 Left Green Not shown 1250 Right Green Not shown1500 Left Green Not shown 1750 Right Green Not shown 2000 Left Green Notshown 2250 Right Green Not shown 2500 Left Green Not shown 2750 RightGreen Not shown 3000 Left Green Not shown 3250 Right Green Not shown3500 Left Green Not shown 3750 Right Green Not shown 4000 Left Yellow 7Fixation Test Cue 4250 Right Yellow 8 Fixation Test Cue 4500 Left Green9 4750 Right Green 10 

FIGS. 11-17 show, in time sequence, a rotating fixation stimulus 500, inaccordance with another embodiment of the invention. A subject mayvisually fixate upon a spiked corona 510, which rotates around a centralcore 520. Although shown with eight regularly arranged spikes 530, thecorona 510, may have a greater or fewer number of spikes 530. The spikesmay be arranged in either a regular or irregular manner around the core520. While a subject's vision may saturate with regard to the unchangingparts of the rotating stimulus 500, the alternating positions of therotating spikes 530 will render at least the spikes 530 continuouslyvisible. A rotating fixation stimulus 500 of altered color (orangecorona 210 with a green core 220), may be used as a test cue 600, and isshown in a base configuration in FIG. 15 and in a rotated, altered,configuration in FIG. 16. The corona may rotate in regular or irregularincrements; in FIGS. 11-17, each increment of rotation is about 28°. Thefollowing table summarizes the illustrative embodiment shown in FIGS.11-17.

In a specific embodiment, the test cue stimulus 600 is closely matchedto the fixation stimulus in terms of luminosity. By closely matching theluminance of the test cue 600 and a fixation stimulus 500, the patient'sfixation may be more precisely ascertained, and consequently, thepatient may be forced to fixate more precisely upon the stimulus 500.Experimental data show that isoluminous test cues are visible onlywithin about 2 degrees of visual angle. Conversely, if the test cue 600varied greatly in luminance from the fixation stimulus 500, then apatient could detect the fixation change at greater angles, e.g., 6°,10°, or even 15° off the line of proper fixation. The luminance of thetest cue 600 may vary from the luminance of the base stimulus 500 by avalue that is 10%, 5% or less of the base pattern luminance. Forexample, a test cue stimulus 600 may cycle between colors that aredistinguishable when substantially isoluminous; e.g., a yellow test cuestimulus stimulus 600 having a luminance of 200 millicandela per squaremeter and a green fixation stimulus 500 pattern of 190 millicandela persquare meter. Core Time Rotation 520 Corona 510 Corresponding (ms)Position Color Color Figure Comment 0 Base Green Yellow 11 250 AlteredGreen Yellow 12 500 Base Green Yellow 13 760 Altered Green Yellow 141000 Base Green Yellow Not shown 1250 Altered Green Yellow Not shown1510 Base Green Yellow Not shown 1750 Altered Green Yellow Not shown2000 Base Orange Green 15 Fixation Cue 2250 Altered Orange Green 16Fixation Cue 2500 Base Green Yellow 17 Return to Standard FixationStimulus

FIGS. 18 and 19 show yet another embodiment in which a striated dynamicfixation stimulus 700 alternates with time between a positive (FIG. 18)and negative (FIG. 19) form. Low-luminosity areas 710 of the stimulus700 in FIG. 18 have a high luminosity in FIG. 19. Conversely,high-luminosity areas 720 of the stimulus 700 in FIG. 18 have a lowluminosity in FIG. 19. The stimulus 700 may repeatedly alternate betweenthese positive and negative forms. If plotted versus time, the displayedluminosity of a given point or area within the stimulus 700 may vary ina square wave, sine wave (which would necessitate the use ofintermediate shades of gray), or other repetitive pattern to allowalternate resensitization of saturated retinal regions. As in thepreceding examples of FIGS. 4-17, the cycle frequency can vary, but maybe optimal when above 0.5 Hz since retinal desensitization may occurafter less than one second of stimulation. For example, the striationsmay alternate between bright and dark every 250 ms (2 Hz). Thestriations may also continuously or discontinuously rotate around agiven point.

If the striations are sufficiently narrow in width, a subject shouldonly be able to resolve the striations by using the central 1-2° oftheir visual field. As a result, loss of fixation will alter thestriated appearance of the stimulus 700. Thus, the subject will bealerted very quickly if his or her fixation has wandered off target.Additionally, such high resolution features may be used with variousembodiments of the invention as highly accurate test cues since suchtest cues should not be detectable using peripheral vision. Use of thesetest cues may result in increased accuracy in testing subject fixation,and may yield corresponding improvements in testing and trainingresults.

Many variations of the stimulus 700 may be employed. For example,varying colors, patterns or other visually detectable properties may beused, including alternating between more than two such properties (e.g.,changing points or regions from red to yellow, or green). While the useof sine waves and square waves described above implies alterationbetween two fixed levels, the levels may change with time in apre-defined or semi-random manner.

In related embodiments of the present invention, dynamic stimuli likethe dynamic fixation stimuli of FIGS. 1-18 may be used as peripheralspot stimuli for static or kinetic campimetry or perimetry, or as acomponent of visual restoration therapy (e.g., NovaVision VRT™;NovaVision, Inc, Boca Raton, Fla.).

In embodiments, a subject is tasked with fixating on a central fixationstimulus (static or dynamic) and responding to the appearance of aperipheral spot stimulus. The peripheral spot stimulus has a movementelement to the presentation to cause preferential detection by themotion sensitive portion of the visual pathway (a “dynamic peripheralstimulus”). However, the peripheral spot stimulus is still a “spot” inthe sense that is presented within bounds that define a fraction of thevisual field comparable to the fraction of a visual field that might bestimulated by a static spot stimulus. Thus, the stimulus may be ananimation within narrowly defined bounds, i.e., bounds that aresubstantially less than the visual field of the subject. For example,the bounds may correspond to 5%, 3%, or 1% or the patient's visualfiled. The dynamic peripheral stimulus may be a single spot or coherentgroup of spots or objects. The stimulus may be adjustable in size,brightness, hue, frequency or other parameter. The dynamic peripheralstimulus may be used to map the visual field through perimetry orcampimetry, to stimulate visual field region in a visual restorationtherapy session, or both. Accordingly, user input may be collected toindicate perception of the dynamic peripheral spot stimuli.

FIG. 20 is a flow diagram for a presentation of the dynamic peripheralspot stimulus. A peripheral location in which the dynamic peripheralspot stimulus is to be applied is selected (step 800). The location maybe based on a previous perimetry or campimetry. For example, the borderof the motion-sensitive visual field may be determined using kineticperimetry. Motion sensitive visual-field regions on, near or within thisborder may then be tested or stimulated for therapeutic purposes usingthe dynamic peripheral spot stimulus. The overall size of the stimulusmay occupy a relatively small fraction of the visual field to increasecampimetry resolution or therapeutic specificity. For example, theboundary of the stimulus may consist of 10-20 pixels on a computerizeddisplay.

A base peripheral stimulus is presented at the selected location (step810). Like the above-described fixation stimuli, the stimulus is thenaltered to target a different retinal region (step 820). The subject'smotion-sensitive visual pathway may detect this alteration. Steps 810and 820 may be repeated a given number of times while awaiting aresponse from the subject (step 830). Optionally, if there is noresponse from the subject an additional characteristic (e.g.,luminosity, contrast, motion frequency, or hue) of the dynamicperipheral stimulus may be altered; when used for campimetry, amultidimensional motion-sensitive visual-field map may be therebycreated. Upon receiving a response from the subject or reaching atime-out or other termination condition, a new location is chosen (step800). This process (steps 800-830) is repeated until a visual-field mapof sufficient detail is created, or until therapy is complete.

By stimulating visual-field regions that do not respond to staticstimuli, dynamic peripheral stimuli may be useful for testing andtreating subjects that have not optimally responded to other stimuli,and for use with patients having extremely poor vision (e.g., end stageglaucoma, optic atrophy, or retinitis pigmentosa). Dynamic peripheralstimulus may be incorporated as a feature into existing perimeters.

EXAMPLE ONE

An isoluminous circular spot of small angular subtense (e.g. 11 pixelson an LCD monitor) is programmed to appear at pre-determined locationswithin the testing or therapy area of the applicable device. Thecircular spot of light “blinks” on and off at a pre-determined frequencybut does not deviate from its original location.

EXAMPLE TWO

Two small (e.g. 5 pixels on an LCD screen), vertically elongatedellipses of light (paired side-by side) appear at a pre-determinedlocation within the testing or therapy area and alternate illuminationat a pre-determined frequency (e.g., right-left-right-left . . . ). Thestimulus is modulated in appearance to trigger the percept of motion butthe stimulus remains fixed in its location until detection or apre-determined length of time.

In another embodiment of the invention, a frequency doubling grating maybe used as a fixation stimulus in a way that creates an opticalillusion. FIG. 21 shows a frequency doubling grating 850 as displayedupon a computer display in a brief moment of time. Like the frequencydoubling gratings used for FDT, the spatial luminosity phase of thefrequency doubling grating 850 is cycled above the critical flickerfrequency, e.g., 25 Hz, to create a frequency doubling optical illusion.FIG. 22 shows how such an optical illusion might appear to a healthysubject. Unlike prior art gratings, however, the grating 850 of FIGS.21-22 is used as a fixation stimulus, rather than a peripheral teststimulus. Peripheral stimuli used in connection with the grating 850 maybe any of those described herein, among others. By appropriately tuningthe frequency doubling grating 850, the frequency doubling opticalillusion will only be visible to a subject if it illuminates the verycentral portion of the subject's retina. As a result, very smalldeviations in fixation will be noticeable to the subject and testablevia an appropriate test cue (e.g., a change in the orientation, or otherdetectable change in the grating 850). For example, due to the structureof the human visual system, movement of the patient's fixation be aslittle as 2° will result in about a 50% decrease in spatial resolution.With an appropriately configured frequency doubling grating 850, thestandard deviation in eye position over the course of therapy may beimproved by a factor of about 1-2°. By increasing the mean accuracy offixation in this manner, the precision and effectiveness of peripheraltesting or stimulatory treatment may be improved. When such a dynamicstimulus is used in visual restoration therapy, a greater fraction ofthe peripheral stimuli may thereby be correctly allocated to appropriatevisual field regions.

Due to disease, injury, genetic or other source of variation, differentsubjects vary in terms of their spatial resolution ability. Therefore,an individualized spatial frequency tuning may be beneficial beforebeginning testing or training. By tuning the spatial frequency of thegrating 850, the subject will be forced to maintain a tighter fixation.FIG. 23 shows a flow chart for a tuning process in accordance with anembodiment of the invention. A spatial frequency parameter controls thespatial frequency of the grating 850 presented on a computerizeddisplay. This parameter is initialized to a low frequency startingpoint, e.g., one that can be detected as frequency doubling illusion bya majority, e.g. 90%, of patients or greater (step 910). The grating 850is then presented as a frequency doubling fixation stimulus (step 920).If the subject detects the illusion (decision step 930), the spatialfrequency parameter is increased and the higher frequency grating 850 ispresented again at step 920. This process is repeated until a thresholdfrequency is reached at which the individual striations of the grating850 are no longer detectable (decision step 930). The spatial frequencyparameter is then decreased to one that is just below the thresholdfrequency. Accordingly, the spatial frequency adjusted stimulus is thendetectable by the subject only with use of the most spatially sensitiveregion of the subject's visual field. For example, the frequencyparameter may be set to be between 2% and 15% lower than the thresholdfrequency.

Since the grating 850 is presented at a high flicker rate, the subject'sretina may be desensitized to the striations. To avoid desensitization,the grating 850 may be systematically perturbed to alternately stimulatedifferent retinal regions; e.g., rotated or translated, as in theembodiments described with reference to FIGS. 1-19. The grating 850 mayalso be alternated with a fixation test cue, also described above.

In alternative embodiments, the disclosed methods for vision fixation,testing and training may be implemented as a computer program productfor use with a computer system. Such implementations may include aseries of computer instructions fixed either on a tangible medium, suchas a computer readable medium (e.g., a diskette, CD-ROM, ROM, or fixeddisk) or transmittable to a computer system, via a modem or otherinterface device, such as a communications adapter connected to anetwork over a medium. The medium may be either a tangible medium (e.g.,optical or analog communications lines) or a medium implemented withwireless techniques (e.g., microwave, infrared, laser or othertransmission techniques). The series of computer instructions embodiesall or part of the functionality previously described herein withrespect to the system. Those skilled in the art should appreciate thatsuch computer instructions can be written in a number of programminglanguages for use with many computer architectures or operating systems.

Furthermore, such instructions may be stored in any memory device, suchas semiconductor, magnetic, optical or other memory devices, and may betransmitted using any communications technology, such as optical,infrared, microwave, laser or other transmission technologies. It isexpected that such a computer program product may be distributed as aremovable medium with accompanying printed or electronic documentation(e.g., shrink wrapped software), preloaded with a computer system (e.g.,on system ROM or fixed disk), or distributed from a server or electronicbulletin board over the network (e.g., the Internet or World Wide Web).Of course, some embodiments of the invention may be implemented as acombination of both software (e.g., a computer program product) andhardware. Still other embodiments of the invention are implemented asentirely hardware, or entirely software (e.g., a computer programproduct).

The described embodiments of the invention are intended to be merelyexemplary and numerous variations and modifications will be apparent tothose skilled in the art. All such variations and modifications areintended to be within the scope of the present invention as defined inthe appended claims.

1. A method for creating a dynamic fixation stimulus for maintainingvisual fixation of a human subject, the method comprising: (a)providing, for the subject to visually fixate upon, a fixation stimulusdisplayed upon a computer-driven display; and (b) altering at least onecharacteristic of the fixation stimulus to allow resensitization of aretina of the subject; so as to allow prolonged visual fixation.
 2. Amethod in accordance with claim 1, wherein the at least onecharacteristic is selected from the group consisting of spatial locus,size, luminosity, and color.
 3. A method in accordance with claim 1,further comprising: (c) repeating steps (a) and (b) for a given numberof cycles.
 4. A method in accordance with claim 3, further comprising:(d) presenting a fixation test cue; and (e) recording the subject'sinput in response to the test cue.
 5. A method in accordance with claim4 comprising performing steps (a)-(e) and repeating step (c) withirregular timing, thereby preventing the subject from reliablypredicting the time at which the fixation test cue is presented.
 6. Amethod in accordance with claim 4 further comprising altering thefixation test cue to allow resensitization of the patient's retina.
 7. Amethod in accordance with claim 1 wherein the alteration of the fixationstimulus is detectable only by an area of the subject's retinacorresponding to less than 2 degrees of the subject's central visualfield.
 8. A method in accordance with claim 1, wherein the dynamicfixation stimulus comprises a repetitively translating object.
 9. Amethod in accordance with claim 1, wherein the fixation stimuluscomprises a rotating object.
 10. A method in accordance with claim 1,wherein the fixation stimulus comprises at least first set and a secondset of objects, the objects of the first and second sets beingintermingled and contrasting, wherein at least a subset of the objectschange appearance over time.
 11. A method in accordance with claim 10,wherein the subset of objects change appearance over time in a cyclicalmanner.
 12. A method in accordance with claim 10, wherein the change inappearance is a change in luminosity.
 13. A method in accordance withclaim 10, wherein the first and second set of objects include sets ofstriations.
 14. A method in accordance with claim 1, further comprisingpresenting peripheral stimuli for purposes of testing or treatment. 15.A computer system for visual fixation, the system comprising: (a) meansfor providing, for the subject to visually fixate upon, a fixationstimulus displayed upon a computer-driven display; and (b) means foraltering the fixation stimulus to allow resensitization of the subject'sretina; thereby allowing prolonged visual fixation upon the resultingdynamic fixation stimulus.
 16. A computer system according to claim 15,further comprising: (c) means for repeating steps (a) and (b) for agiven number of cycles.
 17. A computer system according to claim 16,further comprising: (d) means for presenting a fixation test cue; and(e) means for recording the subject's input in response to the test cue.18. A computer system in accordance with claim 17, comprising means forperforming steps (a)-(e) and repeating step (c) with irregular timing,thereby preventing the subject from reliably predicting the time atwhich the fixation test cue is presented.
 19. A computer system inaccordance with claim 18 further comprising means for altering thefixation test cue to allow resensitization of the subject's retina. 20.A computer program product for use on a computer system for allowing asubject to extendedly fixate upon on computer-based fixation target, thecomputer program product comprising a computer usable medium havingcomputer readable program code thereon, the computer readable programcode including: (a) program code for providing, for the subject tovisually fixate upon, a target focal stimulation displayed upon acomputer-driven display; and (b) program code for altering the focalstimulation to allow resensitization of the subject's retina; therebyallowing prolonged visual fixation.